Chapter 5 The Periodic Table Section 5.1 Organizing the Elements Section 5.2 The Modern Periodic Table Section 5.3 Representative Groups

Section 5.1 Organizing the Elements The Search for Order The placement of elements on the periodic table reveals the link between the atomic structure of elements and their properties.

Section 5.1 Organizing the Elements The Search for Order As # of known elements grew, the need to organize them did also. Antoine Lavoisier (1789), French chemist: grouped known elements into categories: metals, nonmetals, gases, and earths Dmitri Mendeleev, Russian chemist/teacher: found a way to organize the elements

Section 5.1 Organizing the Elements Mendeleev’s Periodic Table: Mendeleev’s Proposal Used deck of cards (4 columns); break the elements into rows Key Concept: Mendeleev arranged the elements into rows in order of increasing mass so that elements with similar properties were in the same column.

Section 5.1 Organizing the Elements Mendeleev’s Proposal Periodic table-an arrangement of elements in columns, based on a set of properties that repeat from row to row

Section 5.1: Organizing the Elements Mendeleev’s Prediction Some elements that had not been discovered yet, he left spaces for; also predicted the properties for them

Mendeleev’s Table of Elements (1872) Figure 3 Mendeleev’s Table of Elements (1872)

Section 5.1 Organizing the Elements Evidence Supporting Mendeleev’s Table Key Concept: The close match between Mendeleev’s predictions and the actual properties of new elements showed how useful his periodic table could be.

Section 5.1 Organizing the Elements Evidence Supporting Mendeleev’s Table With the periodic table, chemists could do more than predict properties of new elements They could explain the chemical behavior of different groups of elements

Section 5.2 The Modern Periodic Table The Periodic Law You can use the modern periodic table to classify elements and to compare their properties. Key Concept: In the modern periodic table, elements are arranged by increasing atomic number (# of protons)

Periodic Table of Elements Figure 7 Periodic Table of Elements

Section 5.2 The Modern Periodic Table The Periodic Law: Periods Period-each row in the table of elements # of elements per period varies b/c # of orbitals increases from energy level to energy level Ex. Period 1 (H and He); Period 2 (Li, Be, B, C, N, O, F, and Ne)

Section 5.2 The Modern Periodic Table The Periodic Law: Groups Group-each column on the periodic table Key Concept: Properties of elements repeat in a predictable way when atomic numbers are used to arrange elements into groups.

Section 5.2 The Modern Periodic Table The Periodic Law: Groups Elements in group have same electron configuration **Electron configuration determines element’s chemical properties Members of a group have similar chemical properties Periodic law-pattern of repeating properties

Section 5.2 The Modern Periodic Table Atomic Mass Key Concept: Atomic mass is a value that depends on the distribution of an element’s isotopes in nature and the masses of those isotopes.

Section 5.2 The Modern Periodic Table Atomic Mass: Atomic Mass Units To have a simple way to compare the masses of atoms, scientists chose 1 isotope to serve as a standard. Assigned 12 atomic units to carbon-12 atom (6 protons and 6 neutrons) **Atomic mass unit (amu)-one twelfth of a carbon-12 atom

Section 5.2 The Modern Periodic Table Atomic Mass: Isotopes of Chlorine and Weighted Averages Most elements exist in nature exist as a mix of 2 or more isotopes. 2 natural isotopes of chlorine (Chlorine-35 and Chlorine-37); Chlorine 37 has more neutrons (greater mass) Atomic mass of 35.453; atomic masses of the isotopes get averaged together

Figure 9 Isotopes of Chlorine

Section 5.2 The Modern Periodic Table Classes of Elements Periodic table- 3 ways to classify elements Solids (black), liquids (purple), or gases (red) Elements are divided into those that occur naturally (1-92) and those that don’t (93 and higher) Based on general properties: Key Concept: Elements are classified as metals, nonmetals, and metalloids.

Periodic Table of Elements Figure 7

Section 5.2 The Modern Periodic Table Classes of Elements: Metals (Blue) Def.-elements that are good conductors of electric current and heat. Majority of elements are metals. Some extremely reactive, some don’t react easily Transition metals (Groups 3-12)-elements that form a bridge b/t the elements on the left and right sides of the periodic table

Section 5.2 The Modern Periodic Table Classes of Elements: Nonmetals (Yellow/Orange) Have properties opposite of metals Def.-elements that are poor conductors of heat and electric current Have low boiling points=many are gas at room temp.

Section 5.2 The Modern Periodic Table Classes of Elements: Metalloids (Green) Def.-elements with properties that fall between those of metals and nonmetals Ability to conduct electric current varies with temperature.

Section 5.2 The Modern Periodic Table Variation Across a Period Key Concept: Across a period (row) from left to right, the elements become less metallic and more nonmetallic in their properties. Most reactive metals-left side Most reactive nonmetals-right side

Periodic Table of Elements Figure 7 Periodic Table of Elements

Section 5.3 Representative Groups Valence Electrons The # of an A group matches the # of valence electrons in an electron configuration for an element in that group. Def.-an electron that is in the highest occupied energy level of an atom

Section 5.3 Representative Groups Valence Electrons Valence electrons play a key role in chemical reactions. **Properties vary across a period (row) b/c the number of valence electrons increases from left to right. Key Concept: Elements in a group have similar properties because they have the same number of valence electrons.

Periodic Table of Elements Figure 7

Section 5.3 Representative Groups The Alkali Metals-Group 1A Li, Na, K, Rb, Cs, Fr Have one valence electron Are extremely reactive; found in nature only as compounds Key Concept: The reactivity of alkali metals increases from the top of Group 1A to the bottom.

Section 5.3 Representative Groups The Alkaline Earth Metals-Group 2A Be, Mg, Ca, Sr, Ba, Ra Have 2 valence electrons Harder than Group 1A metals Key Concept: Differences in reactivity among the alkaline earth metals are shown by the ways they react with water (ex. Ca, Sr, Ba-cold water) and (Mg-hot water) Mg & Ca-essential for biological functions and provide materials used in construction and transportation

Section 5.3 Representative Groups The Boron Family-Group 3A Have 3 valence electrons B, Al, Ga, In, Tl Key Concept: Aluminum is the most abundant metal in Earth’s crust. Al-car parts, packaging, airplanes B-glass that does not shatter easily w/ rapid temp. change (lab glassware)

Section 5.3 Representative Groups The Carbon Family-Group 4A C, Si, Ge, Sn, Pb Have 4 valence electrons Metallic nature of group increases from top to bottom (conductivity) Life on Earth would not exist w/o Carbon Key Concept: Except for water, most of the compounds in your body contain carbon. Silicon-the 2nd most abundant element in the Earth’s crust

Section 5.3 Representative Groups The Nitrogen Family-Group 5A N, P, As, Sb, Bi Have 5 valence electrons Includes elements w/ wide range of physical properties N & P-most important Key Concept: Besides nitrogen, fertilizers often contain phosphorus.

Section 5.3 Representative Groups The Oxygen Family-Group 6A O, S, Se, Te, Po Have 6 valence electrons Key Concept: Oxygen is the most abundant element in the Earth’s crust. Complex forms of life need O to live. Ex. Oxygen tanks, ozone layer S-used in fertilizers

Section 5.3 Representative Groups The Halogens-Group 7A F, Cl, Br, I, At Have 7 valence electrons Key Concept: Despite their physical differences, the halogens have similar chemical properties. Pg. 144 Highly reactive nonmetals; reactivity decreases from top to bottom (F) F-prevents tooth decay, Cl-kills bacteria, and I-thyroid gland function

Section 5.3 Representative Groups The Noble Gases-Group 8A He, Ne, Ar, Kr, Xe, Rn He has 2 valence electrons; all other have 8 valence electrons Key Concept: The noble gases are colorless and odorless and extremely unreactive. Ex. Argon-light bulbs; all are used in neon lights except Radon He-pink, Ne orange-red, Ar-lavender, Kr-white, Xe-blue